I. Field of the Invention
This invention relates to the production of a Schottky barrier diode and, more particularly, to a Schottky barrier diode provided with a guard ring region and a method of manufacturing the same.
II. Description of the Prior Art
A rectifying element which makes use of a barrier formed at the interface or junction between a metal and a semiconductor (i.e., a Schottky barrier) is usually called a Schottky barrier diode. With this diode, the forward voltage and also parasitic capacitance are low as compared with the ordinary p-n junction diode, so that it finds extensive applications in ICs and LSICs. However, since the edge of the interface between the metal and semiconductor constituting the Schottky barrier is usually contiguous to an insulating film (mostly oxide film), when a reverse voltage is applied, electric field concentration is liable to occur at the end adjacent to the aforementioned oxide film or charges are likely to be injected into the oxide film. As a result, an inversion layer is formed in a surface region of the semiconductor and the breakdown voltage is significantly lowered.
In order to overcome this drawback, it has been the practice to dope a surface region of the semiconductor substrate contiguous to the oxide film with an impurity of the opposite conductivity type to the conductivity type of the substrate so as to form a guard ring region. The provision of this guard ring region solves the problems of the electric field concentration and charge injection into the oxide film mentioned above. A Schottky barrier diode provided with such a guard ring region is usually produced in the manner as shown in FIG. 1. As is shown, on the surface of a semiconductor substrate 1, for instance of n-conductivity type, is formed an oxide film 2 by thermal oxidation. The oxide film 2 is then photoetched to form an opening 3 partly exposing the surface of the substrate 1. Then, the exposed surface region of the substrate is doped with a p-type impurity along the side wall of the oxide film 2 defining the opening 3 to form a guard ring region 4. Thereafter, a metal layer is selectively vapor deposited on the semiconductor substrate surface portion within the opening 3 and is converted to a silicide layer 5 through a thermal treatment. Finally, an aluminum lead layer 6 is formed to complete the Schottky barrier diode.
In the above prior art method, however, mask alignment is necessary for doping with the p-type impurity in the step of forming the guard ring region 4. This means that an extra allowance or margin has to be provided for the mask alignment in the layout of the opening 3 in the oxide film, thus increasing the area of the Schottky barrier region and reducing the integration density.